SmartMirror-Projektarbeit/node_modules/keyv/README.md

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	<img width="250" src="https://rawgit.com/lukechilds/keyv/master/media/logo.svg" alt="keyv">
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> Simple key-value storage with support for multiple backends

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Keyv provides a consistent interface for key-value storage across multiple backends via storage adapters. It supports TTL based expiry, making it suitable as a cache or a persistent key-value store.

## Features

There are a few existing modules similar to Keyv, however Keyv is different because it:

- Isn't bloated
- Has a simple Promise based API
- Suitable as a TTL based cache or persistent key-value store
- [Easily embeddable](#add-cache-support-to-your-module) inside another module
- Works with any storage that implements the [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) API
- Handles all JSON types plus `Buffer`
- Supports namespaces
- Wide range of [**efficient, well tested**](#official-storage-adapters) storage adapters
- Connection errors are passed through (db failures won't kill your app)
- Supports the current active LTS version of Node.js or higher

## Usage

Install Keyv.

```
npm install --save keyv
```

By default everything is stored in memory, you can optionally also install a storage adapter.

```
npm install --save @keyv/redis
npm install --save @keyv/mongo
npm install --save @keyv/sqlite
npm install --save @keyv/postgres
npm install --save @keyv/mysql
```

Create a new Keyv instance, passing your connection string if applicable. Keyv will automatically load the correct storage adapter.

```js
const Keyv = require('keyv');

// One of the following
const keyv = new Keyv();
const keyv = new Keyv('redis://user:pass@localhost:6379');
const keyv = new Keyv('mongodb://user:pass@localhost:27017/dbname');
const keyv = new Keyv('sqlite://path/to/database.sqlite');
const keyv = new Keyv('postgresql://user:pass@localhost:5432/dbname');
const keyv = new Keyv('mysql://user:pass@localhost:3306/dbname');

// Handle DB connection errors
keyv.on('error', err => console.log('Connection Error', err));

await keyv.set('foo', 'expires in 1 second', 1000); // true
await keyv.set('foo', 'never expires'); // true
await keyv.get('foo'); // 'never expires'
await keyv.delete('foo'); // true
await keyv.clear(); // undefined
```

### Namespaces

You can namespace your Keyv instance to avoid key collisions and allow you to clear only a certain namespace while using the same database.

```js
const users = new Keyv('redis://user:pass@localhost:6379', { namespace: 'users' });
const cache = new Keyv('redis://user:pass@localhost:6379', { namespace: 'cache' });

await users.set('foo', 'users'); // true
await cache.set('foo', 'cache'); // true
await users.get('foo'); // 'users'
await cache.get('foo'); // 'cache'
await users.clear(); // undefined
await users.get('foo'); // undefined
await cache.get('foo'); // 'cache'
```

### Custom Serializers

Keyv uses [`json-buffer`](https://github.com/dominictarr/json-buffer) for data serialization to ensure consistency across different backends.

You can optionally provide your own serialization functions to support extra data types or to serialize to something other than JSON.

```js
const keyv = new Keyv({ serialize: JSON.stringify, deserialize: JSON.parse });
```

**Warning:** Using custom serializers means you lose any guarantee of data consistency. You should do extensive testing with your serialisation functions and chosen storage engine.

## Official Storage Adapters

The official storage adapters are covered by [over 150 integration tests](https://travis-ci.org/lukechilds/keyv/jobs/260418145) to guarantee consistent behaviour. They are lightweight, efficient wrappers over the DB clients making use of indexes and native TTLs where available.

Database | Adapter | Native TTL | Status
---|---|---|---
Redis | [@keyv/redis](https://github.com/lukechilds/keyv-redis) | Yes | [![Build Status](https://travis-ci.org/lukechilds/keyv-redis.svg?branch=master)](https://travis-ci.org/lukechilds/keyv-redis) [![Coverage Status](https://coveralls.io/repos/github/lukechilds/keyv-redis/badge.svg?branch=master)](https://coveralls.io/github/lukechilds/keyv-redis?branch=master)
MongoDB | [@keyv/mongo](https://github.com/lukechilds/keyv-mongo) | Yes | [![Build Status](https://travis-ci.org/lukechilds/keyv-mongo.svg?branch=master)](https://travis-ci.org/lukechilds/keyv-mongo) [![Coverage Status](https://coveralls.io/repos/github/lukechilds/keyv-mongo/badge.svg?branch=master)](https://coveralls.io/github/lukechilds/keyv-mongo?branch=master)
SQLite | [@keyv/sqlite](https://github.com/lukechilds/keyv-sqlite) | No | [![Build Status](https://travis-ci.org/lukechilds/keyv-sqlite.svg?branch=master)](https://travis-ci.org/lukechilds/keyv-sqlite) [![Coverage Status](https://coveralls.io/repos/github/lukechilds/keyv-sqlite/badge.svg?branch=master)](https://coveralls.io/github/lukechilds/keyv-sqlite?branch=master)
PostgreSQL | [@keyv/postgres](https://github.com/lukechilds/keyv-postgres) | No | [![Build Status](https://travis-ci.org/lukechilds/keyv-postgres.svg?branch=master)](https://travis-ci.org/lukechildskeyv-postgreskeyv) [![Coverage Status](https://coveralls.io/repos/github/lukechilds/keyv-postgres/badge.svg?branch=master)](https://coveralls.io/github/lukechilds/keyv-postgres?branch=master)
MySQL | [@keyv/mysql](https://github.com/lukechilds/keyv-mysql) | No | [![Build Status](https://travis-ci.org/lukechilds/keyv-mysql.svg?branch=master)](https://travis-ci.org/lukechilds/keyv-mysql) [![Coverage Status](https://coveralls.io/repos/github/lukechilds/keyv-mysql/badge.svg?branch=master)](https://coveralls.io/github/lukechilds/keyv-mysql?branch=master)

## Third-party Storage Adapters

You can also use third-party storage adapters or build your own. Keyv will wrap these storage adapters in TTL functionality and handle complex types internally.

```js
const Keyv = require('keyv');
const myAdapter = require('./my-storage-adapter');

const keyv = new Keyv({ store: myAdapter });
```

Any store that follows the [`Map`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) api will work.

```js
new Keyv({ store: new Map() });
```

For example, [`quick-lru`](https://github.com/sindresorhus/quick-lru) is a completely unrelated module that implements the Map API.

```js
const Keyv = require('keyv');
const QuickLRU = require('quick-lru');

const lru = new QuickLRU({ maxSize: 1000 });
const keyv = new Keyv({ store: lru });
```

The following are third-party storage adapters compatible with Keyv:

- [quick-lru](https://github.com/sindresorhus/quick-lru) - Simple "Least Recently Used" (LRU) cache
- [keyv-file](https://github.com/zaaack/keyv-file) - File system storage adapter for Keyv
- [keyv-dynamodb](https://www.npmjs.com/package/keyv-dynamodb) - DynamoDB storage adapter for Keyv

## Add Cache Support to your Module

Keyv is designed to be easily embedded into other modules to add cache support. The recommended pattern is to expose a `cache` option in your modules options which is passed through to Keyv. Caching will work in memory by default and users have the option to also install a Keyv storage adapter and pass in a connection string, or any other storage that implements the `Map` API.

You should also set a namespace for your module so you can safely call `.clear()` without clearing unrelated app data.

Inside your module:

```js
class AwesomeModule {
	constructor(opts) {
		this.cache = new Keyv({
			uri: typeof opts.cache === 'string' && opts.cache,
			store: typeof opts.cache !== 'string' && opts.cache,
			namespace: 'awesome-module'
		});
	}
}
```

Now it can be consumed like this:

```js
const AwesomeModule = require('awesome-module');

// Caches stuff in memory by default
const awesomeModule = new AwesomeModule();

// After npm install --save keyv-redis
const awesomeModule = new AwesomeModule({ cache: 'redis://localhost' });

// Some third-party module that implements the Map API
const awesomeModule = new AwesomeModule({ cache: some3rdPartyStore });
```

## API

### new Keyv([uri], [options])

Returns a new Keyv instance.

The Keyv instance is also an `EventEmitter` that will emit an `'error'` event if the storage adapter connection fails.

### uri

Type: `String`<br>
Default: `undefined`

The connection string URI.

Merged into the options object as options.uri.

### options

Type: `Object`

The options object is also passed through to the storage adapter. Check your storage adapter docs for any extra options.

#### options.namespace

Type: `String`<br>
Default: `'keyv'`

Namespace for the current instance.

#### options.ttl

Type: `Number`<br>
Default: `undefined`

Default TTL. Can be overridden by specififying a TTL on `.set()`.

#### options.serialize

Type: `Function`<br>
Default: `JSONB.stringify`

A custom serialization function.

#### options.deserialize

Type: `Function`<br>
Default: `JSONB.parse`

A custom deserialization function.

#### options.store

Type: `Storage adapter instance`<br>
Default: `new Map()`

The storage adapter instance to be used by Keyv.

#### options.adapter

Type: `String`<br>
Default: `undefined`

Specify an adapter to use. e.g `'redis'` or `'mongodb'`.

### Instance

Keys must always be strings. Values can be of any type.

#### .set(key, value, [ttl])

Set a value.

By default keys are persistent. You can set an expiry TTL in milliseconds.

Returns `true`.

#### .get(key)

Returns the value.

#### .delete(key)

Deletes an entry.

Returns `true` if the key existed, `false` if not.

#### .clear()

Delete all entries in the current namespace.

Returns `undefined`.

## License

MIT © Luke Childs